Mechanism behind solution color change due to pH change

[Baho Ilok]

I would like to ask for somebody to point me in the right direction - any literature I could read - regarding the mechanism behind color changes that an organic solution undergoes due to changes in pH. I am not referring to organic indicators or dyes, specifically. I have observed in my experiments that a certain polysaccharide solution is colorless at pH ≤ 6 and gradually turns yellowish-green as pH is increased to 11 at room temperature. I was wondering if there is an explanation for this phenomenon that relates to the compound's structure (i.e. presence of certain functional groups).

Thanks!

 

[HAYAO]

Well there are plenty of types of Polysaccharides. You'll have to be more specific in order for people to give you a good answer.
But I think it is obvious from the basic chemical structure of Polysaccharides with a lot of hydroxyl groups that it is sensitive to higher region of pH.

 

[Baho Ilok]

You'll have to be more specific in order for people to give you a good answer.

In my experiments, I use the hemicellulose xylan from corn core. I know of its structure but the mechanism by which its solution changes from colorless to yellowish-green from acidic to basic pH is what I would like to know. Thanks!

 

[HAYAO]

In my experiments, I use the hemicellulose xylan from corn core. I know of its structure but the mechanism by which its solution changes from colorless to yellowish-green from acidic to basic pH is what I would like to know. Thanks!

Okay, is the xylan "pure" xylan? Or are there substituents on it? I don't know what xylan looks like when taken from corn core.

Also, what are you using to change the pH?

 

[Ygggdrasil]

Is the color change reversible? Could be the same chemical reaction that leads to the yellowing of paper (i.e. oxidation of lignins that often accompany cellulose harvested from plant sources). See http://gizmodo.com/why-old-paper-turns-yellow-1692099465 for more info.